Process for making cellulose sponge



April 28, 1954 w. c. RICHARDSON ETAL 3,131,076

PRocEss FOR MAKING cELLuLosE sPoNGE WILLIAM CRICHARDSON RICHARD J.BOH NHOFF BY THEIRATTORNEYS April 28, 1964 w. c. RICHARDSON ETAL 3,131,076

PROCESS FOR MAKING CELLULOSE SPONGE FREE NGOH, Wf.% ON VISCOSE WILLIAM C. RICHARDSON RICHARD J, BOHNHOFF BY THEIR ATTORNEYS United States Patent Gli ice PRUCESS FSR Q CELLULOSE SP-ONGE C. Richardson, lvlohile, and Richard 3. Bohnho,

Loxiey, Ala., assignors, by mesne assignments, to

Courtaulds, Limited, London, England, a British company Filed May il, 1961, Ser. No. 107,838 1 Claim. (Cl. 10E-4122) This invention relates to the Imanufacture of cellulose sponge and in particular to a method for making cellulose :sponge of improved strength.

Cellulose sponge is conventionally made by mixing together viscose, a crystalline pore forming material, and cellulose liber. The pasty mixture :is then placed in a mold and heated. The viscose is regenerated, and the crystalline pore former is melted or dissolved, leaving the sponge product.

The function of the fibers in the sponge mix is to provide strength and cohesiveness. To do this, however, the iibers must be evenly dispersed throughout the original viscose. Unfortunately it has been found that when the liber-s are put into the viscose they do not disperse, but on th contrary tend to agglomerate and form clumps.

To `overcome this tendency it has been proposed to add complex wetting and dispersing agents to the viscose. However, suc-h agents are expensive and may have an undesirable eect on the finished produc-t.

it is well known that celluloslc fibers swell in various reagents such as caustic soda, zinc chloride, and the like. lt is also known that the degree of swelling is a function `of the specilic Jliber treated, the swelling agent used and the swelling agent concentration. Further it has been found that for any particular ber and swelling agent there is a concentration of swelling agent at which maximum swelling of the liber occurs.

Now viscose, which is an alkaline medium containing free NaOH, is itself a swelling agent for cellulose. How. ever, viscose normally used for Isponge-making contains not more than say 10% total NaOH, i.e. free and combined as lsodium cellulose xanthate or" which not more than about 7% will be free. Usually the viscose will contain on the order of l to 8% total NaOH of which say 1% to will be free NaOH. Such concentrations are not high enough to er'ect maximum swelling of cellulose tibers, and as noted above when :tibers are put into normal viscose they tend to form clumps and aggregates. It has now been discovered, however, that when the swelling agent concentration is raised -to a level corresponding to the co centration at vhieh maximum swelling of the fibers in the viscose occurs, la smooth yber dispersion is obtained and sponge products having improved strength result.

The invention therefore comprises, in a process for making cellulose sponge wherein viscose, cellulose reinforcing lbers and a pore-forming substance are combined to form a vsponge mix, which is thereafter coagulated regenerate? to form a sponge structure, `the improvement which comprises addinc a swelling agent to the mix to give a concentration corresponding approximately to the concentra-tion at which maximum swelling occurs. Normally the swelling agent concentration used 3,l3l, 76 Patented Apr. 28, 1964 will be within 1% (i- 1%) of the concentration at which maximum swelling occurs.

In the drawings:

FlG. 1 is a graph showing the effect of swelling agent concentration in viscose on .the swelling of cotton liber and the tenacity of sponge made therefrom.

FlG. 2 is a graph showing the eect of swelling agent concentration in viscose on the swelling of ram-ie libe-r and the tenacity of sponge made therefrom.

As noted above, conventional cellulose sponge paste contains viscose, rein-forcing ber and a pore forming agent.

The viscose may be any conventional type customarily used for liber forming purposes. lt will usually, but not necessarily, contain 5-9% by weight cellulose, and 4.5- 6.5% by weight total NaOH. lt mi y be aged or unaged, and have a gamma number of say 20 to 50.

The liber used may be any cellulosic liber, normally a natural cellulosic iiber such as cotton, ramie, jute or llax.

The pore forming agent is conventionally sodium sulfate. Glaubers salt (NaZS-OglQHZO) is normally used, though the anhydrous salt may also be used if desired. 'here is, however, no advantage in using the anhydrous material. in place of sodium sulfate, other fusible, water soluble sdts that do not readily regenerate viscose may -be used, as may gas forming substances such as aluminum powder.

The cellulose swelling agent may be any of a large variety or materials including the alkali metal hydroxides, the alkali metal salts of weak acids, e.g. sodium Zincate, salts of Weak bases `and strong acids such las zinc chloride and zinc nitrate yand the like. Sodium hydroxide is, however, much preferred since it is a very effective swelling agent and introduces no new elements into the sponge making mixture.

The proportions of viscose, fiber and pore forming material in the mixture may vary within wide limits. In general, however, for `one part by weight of viscose, beytween about 0.05 and `about 0.15 pant of iiber and about 2 to 7 par-ts of pore forming agent are used.

The partide size of the pore forming agent is not especially critical and will depend to some extent on the size or the pores desired. A normal range would be from say tine dust to 1/2.

As noted above, the concentration of swelling agent lat which maximum swelling occurs, depends on the liber and the agent. In the case or" caustic soda, with most natural cellulose fibers, maximum swelling is obtained in vise-ose containing `from 9 to 12% free NaOH.

In carrying out the invention it may be desirable to determine the maximum swelling concentration -for the particular fiber, visc se and swelling agent to be used. This may be `done by taking samples of the fiber, loading the individual r'ibers with an appropriate weight, immersing the bers in viscose containing varying amounts of the swelling agent for say 3G minutes and then measuring the length of fiber. As Marsh (Mercerization, Chapman-Hall, London, 1941) has shown, longitudinal `contnaotion is an index of cross-sectional swelling and the concentration of swelling agent which gives maximum lcontraction corresponds to the concentration for maximum swelling.

The procedural steps necessary to make sponge in accordance with the invention are entirely conventional.

3 The viscose and swelling agent are normally mixed together and lthe fiber then added. As the fiber lis added to the viscose and swelling agent the eiect or" reaching a maximtun swelling is clearly visible. Clumps of fiber break up and a smooth dispersion is obtained.

The form in which the swelling agent is added is not of major significance. Preferably, however, it is added as an aqueous solution of moderate concentration, say 25 to 50%, by Weight. The viscose-fiber mass is normally highly viscous `and the additional water aids in obtaining an even mixture without excessive stirring as well as avoiding high local concentrations of swelling agent. On the other hand, too much water is undesirable in causing dissolution and waste :of pore former. Generally not more than about 0.15 parts of water, per part of viscose is added with the swelling agent.

After mixing, the paste or mix is put into a mold or poured on `a slab and heated to say 90 to 100 C. to regenerate the viscose. After regeneration the sponge is washed thoroughly to remove pore former and is then ready for use.

'The invention will be vfurther `described by means of the yfollowing specific examples which are given for purposes of illustration only and are not to be taken as in any Way limiting the invention beyond the scope of the appended claim.

EXAMPLE I To samples of viscose containing 8.75% cellulose and 5.0% NaOH (3.0% bound NaOH) were added varying amounts of NaOH as a 50% aqueous solution to give free caustic concentrations varying from about 5 to about 13% by weight. Cotton bens approximately 2.5 cm. long were loaded with 50 mg. weights and immersed in the viscose samples Vfor 30 minutes. The change in length Iwas measured in situ. The contraction divided by the original lengthX 100 was recorded as percent contraction and -appears in the appropriate column of Table 1 below.

Viscose samples containing varying amounts of NaOH were next used to make sponge. The mix was prepared by adding the required lamount of sodium hydroxide as 50% aqueous solution to the viscose, while stirring. The bers were next 4added in the proportion of 0.07 part by weight of ber to one part of viscose. Finally the .sodium sulphate (Na2SO4.10H2O) was added, using a particle size through a 0.635 cm. sieve. About 5 parts of Na2SO4.10H2O were used per part of viscose. After the paste was thoroughly knea'ded it was placed in stainless molds dined with polyethylene `and having perforated bottoms.

The molds and `samples were then placed in a covered container and low pressure steam introduced for 30 minutes maintaining `a temperature of about 100 C. The samples were then removed from the molds, Washed in cold water, bleached, washed and dried.

To determine tenacity, a strip yof the product 2.54 cm. x 4.81 cm. long x about 0.6 cm. thick was cut, saturated with water, excess Water removed, and broken on an Instron tester. Cross-head speed was about 1.27 cm./min., gage length 1.27 cm. and chart speed 12.7 cm./min. with `a full scale reading of 25,000 g. The denier vof the strip =was calculated, in accordance with textile practice, as the weight in grams of 9,000 meters and tenacity was reported -as grams to break/ denierX 10. The results obtained are shown in Table 1.

To illustrate the relation between maximum swelling concentration of NaOH and concentration yat which maximum tenacity is attained, the iigures set out in Table 1 were plotted and smooth curves drawn through them. These curves appear in FIG. 1 and as will be seen from that figure, the concentration at which maximum swelling occurs coincides almost exactly with that at which maximum tenacity is obtained.

Table 1 Percent C ontra ctlon Percent free NaOH cowoocncn EXAMPLE II The procedure of Example I was repeated using ramie fiber. The results obtained are `given in Table 2 below and are plotted in FIG. 2. Again maximum swelling concentration corresponds remarkably well to maximum tenacity.

Table 2 Free NaOI-I, Percent Tenacity Percent Contraction We claim:

In the manufacture of cellulose sponge wherein viscose, cellulose reinforcing fibers selected `from the group consisting of cotton fand namie, and a pore-forming substance are combined to form Ea :sponge mix, which is thereafter coagulated and regenerated to form a sponge structure, the improvement -Which comprises adding sodium hydroxide to said mix in an amount to bring the free sodium hydroxide concentration in said mix to between labout 9 and about 12% by Weight and to within about 1% of that necessary to cause maximum swelling of the ber, said additive also being present in a proportion such as :to increase the tenacity of the sponge structure to at least 30% more than that of a lsponge made from said mix Without said addition of sodium hydroxide.

References Cited in the tile of this patent UNITED STATES PATENTS 

